I, too, have been researching the most cost-effective method of making my
'98 faster. Plenty of folks who have a Roe are hitting 600+rwhp on the stock manifolds. The bang for the buck ratio for headers on these cars doesn't seem to be very good at all. The only headers you will find for
$1k will be used, not new (if that matters other than limiting selection).
You won't hit 500rwhp without headwork or Strikers (or N2O), from what I've gathered. Save the $$ you would have put towards headers and wait until you can go FI. That's what I hope to do, anyway.
I am trying to hit 450rwhp once I am done with the current round of mods I am installing over the next month or so. They include hi-flow cats, Borla exhaust, smooth tubes, SCT tune, and 1.7 rockers. I'll post once I get some dyno results. We'll see!